The present invention relates to medical devices, and more particularly to the use of a formable source material having an activatable nuclide in medical devices.
Treatment of various medical conditions, notably cancer, with ionizing radiation is known. In one method of application, sources of gamma (xcex3) radiation, or more recently accelerators producing X-rays or electrons in the approximate energy range of 4 to 20 MeV, are used to direct intense collimated beams of radiation at tumors. To concentrate radiation effects in the tumor while sparing to the greatest possible extent the healthy tissues that usually surround it, multiple cross-firing beams intersecting in the tumor are often used. Because the origin of each beam is commonly at a relatively large distance, e.g., 1 meter, from the tumor, this external beam technique is sometimes referred to as tele- (for distant) therapy. In another method of application, referred to as brachy- (for short) therapy, radioactive sources, encapsulated if necessary to prevent escape of radioactive material into the tissues, are temporarily or permanently implanted in or are closely apposed to the tumor or other target tissue.
Various forms of brachytherapy include interstitial therapy where the sources, sometimes enclosed in needles, tubes or catheters, are physically inserted in the affected tissue; intracavitary therapy where source-containing applicators are introduced into naturally-occurring or artificial body cavities; treatment of certain shallow surface lesions by means of externally applied source-bearing containers often described as xe2x80x9cmoldsxe2x80x9d; intra- or endo-arterial irradiation where radioactive sources are inserted in the interior (lumen) of the affected blood vessels, and combinations or variations of these techniques. The type of source used depends on the particular field of application. Some sources emitting xcex2-radiation only, as examples, can be used for intra-arterial brachytherapy because the targeted region of the arterial wall, which is in contact with the source, is heavily irradiated while tissues farther away than the xcex2-ray range receive little or no dose; furthermore, intra-arterial lesions are usually thin, and their deeper regions can be adequately treated even with relatively non-penetrating xcex2-particles. xcex2-sources on the other hand are less suitable than xcex3-ray sources for irradiation of substantial tumor volumes because large numbers of xcex2-sources must be precisely positioned to ensure that the tumor region is not underdosed if the sources are too far apart nor overdosed if they are too close together.
In interstitial brachytherapy of tumors, which are usually larger than intra-arterial lesions, a wide variety of sources and application methods has been used. The sources and methods of using them are generally familiar to those skilled in the art and include, but are not limited to, radium 226 in equilibrium with its decay products, radon 222, and more recently cobalt 60, cesium 137, gold 198, iridium 192, tantalum 182, iodine 125, palladium 103, and equilibrium mixtures of the xcex2-emitters strontium 90 and yttrium 90, or yttrium 90 alone for specialized sites such as the pituitary gland. The choice of brachytherapy radionuclide will be within the capability of persons skilled in the art and will depend among other factors on the penetrating ability required of the radiation, the radiation emission rate, the half-life, the available activity, the tumor size, shape, location and cellular composition, on the clinical stage to which the tumor has progressed, on the patient""s physical condition, on the experience and skill of the operator, on the availability and ability of assisting staff such as medical physicists and dosimetrists, and most particularly on whether the planned implant is to be temporary or permanent.
Specifically, intra-arterial brachytherapy can be used to prevent regrowth of tissue following the treatment of arteries for occlusive diseases, such as atherosclerosis. A commonly used method for treating atherosclerosis is Percutaneous Transluminal Coronary Angiopiasty (PTCA). PTCA includes insertion of a balloon catheter through an incision in the femoral artery near the groin, advancement of the balloon over the aortic arch, further advancement within the selected coronary artery, continuing until the balloon portion is placed across the narrowed (stenosed) region. The balloon is inflated, widening the stenosed region of the vessel.
After catheter withdrawal, significant vessel reclosure known as xe2x80x9crestenosisxe2x80x9d may develop and largely negate the dilation treatment. The reclosure may occur within hours or days of dilation, but more commonly occurs progressively, within six months of the angioplasty. One approach to dealing with restenosis utilizes stents, which are short tubular sections having a lumen therethrough, placed across the recently dilated vessel region. Stents can be either self-expanding or balloon-expandable. Stents are normally left in place indefinitely, though some versions may be designed for eventual removal. Stents, as any permanently implanted device, may cause long term problems. Because the stent constantly pushes radially outward against the vessel wall, the wall may be adversely affected over long periods, particularly in the regions adjoining the ends of the stent. The use of radiation, delivered to the target region either by external i.e., teletherapeutic means or by use of stents which have been made radioactive, has been suggested, for example by U.S. Pat. Nos. 5,059,166 to Fischell et al. and 5,199,939 to Dake et al. Suitable active stents can be made e.g. by immersing an inactive metal stent coated with a chelating agent in a solution of the desired radioactive material (see, for example, U.S. Pat. No. 5,871,436 to Eury), before insertion in the vascular lumen. Alternatively, the coated stent is immersed in a solution of an unactivated form of the desired nuclide, after which the stent, now bearing inactive material bonded to the metal by the chelator, is exposed to a suitable activating radiation and thereafter inserted in the artery. In yet another method (referred to as ion implantation) of manufacturing radioactive stents, ions of the inactive precursor of the desired radionuclide are driven into the stent surface by means of a high-energy accelerator, after which the stent is activated and inserted in the blood vessel. U.S. Pat. No. 5,873,811 to Wang et al. proposes using an adhesive which includes a radioactive material; the adhesive being applied to the vessel wall region to be treated.
These and other prior art stents have a number of limitations. A primary concern is the potential for leakage of the nuclide from the stent into the blood flowing in the vessel. Avoidance of the release of activated nuclide is often dependent on the quality of joining between the metal surfaces of the stent and the nuclide.
Therefore, an object of the present invention is to provide medical devices having activatable nuclides that are manufactured from materials that are both inexpensively available and easily configured into such devices, and are also permanently or temporarily insertable into the body.
Yet another object of the present invention is to provide medical devices that permit control of the radiation to various vessels and tumors while minimizing damage to tissue not to be treated.
Yet another object of the present invention is to provide devices whose manufacture and use is less hazardous than conventional radioactive devices. There will be less personnel exposure during manufacture because the device is formed before activation, and there is less chance of contamination during use because the radionuclides are integrally bound to the material of the device.
These objects and other objects and advantages are provided by the devices and methods of the present invention. Such devices and methods are useful in the administration of radiation in a wide variety of brachytherapy techniques including treatment of restenosis and of tumors. The present invention provides an integral source material having at least one nuclide that is activatable by exposure to ionizing radiation. The nuclide is a chemically bound constituent of a polymer making up the formable integral source material. Thus, the integral source material can be configured before activation into a medical device or component. Suitable medical devices that can be configured can include, but are not limited to the following: stents, seeds, catheters, irradiator tubes, applicators and molds, enclosures, shrouds, ribbons, rods, beads, needles, obturators, discs and the like, and various combinations thereof.
The activated nuclides can emit various types of radiation that can be used in brachytherapy. Primarily, beta or gamma radiation or a combination thereof is used. It is recognized by those skilled in the art that many secondary radiations accompany these principal emissions, for example, internal conversion, Auger and pair electrons internal and/or external bremsstrahlung, annihilation photons and characteristic x-rays.